Polyethylene terephthalate (PET) is widely used in many materials and products, such as fibers, fabrics, molding resins, and soda bottles. These uses often require a polymer of relatively high molecular weight. Such polymers have been commercially made by raising, either in melt or solid-state polymerization, the molecular weight of a prepolymer or oligomer (i.e., raising the molecular weight of a relatively low molecular weight polymer feedstock). The prepolymer or oligomer is typically prepared by copolymerizing precursor materials, which are typically monomeric units of at least one diacid or diester and at least one glycol, such as, for example, terephthalic acid and ethylene glycol.
Melt polymerizations to high viscosities typically involve expensive plant equipment and require relatively high temperatures, which can accelerate polymer degradation reactions. Typical temperatures for melt polymerizations are between 250 and 310° C. In contrast, solid-state polymerizations are typically run at relatively lower temperatures, typically between temperatures of 160 and 230° C. In addition, solid state polymerizations can result in the production of relatively high molecular weight materials, typically 0.55 dL/g to 1.5 dL/g, compared with melt polymerizations, typically up to 0.65 dL/g. However, in commercial production, solid-state polymerizations may be relatively slow, typically 0.015 to 0.025 dL/g per hour. As a result, there exists a need to enhance the solid state polymerization reactivity to more efficiently produce higher molecular weight polymers.